PM1.0 and PM2.5 characteristics in the roadside environment of Hong Kong

Daily mass concentrations of PM1.0 (particles less than 1.0 mu m in diameter), PM2.5 (particles less than 2.5 mu m in diameter), organic carbon (OC), and elemental carbon (EC) were measured from January through May 2004 at a heavily trafficked sampling site in Hong Kong (PU). The average concentrations for PM1.0 and PM2.5 were 35.9 +/- 12.4 mu g cm(-3) and 52.3 +/- 18.3 mu g cm(-3). Carbonaceous aerosols were the dominant species in fine particles, accounting for similar to 45.7% of PM1.0 and similar to 44.4% of PM2.5. During the study period, seven fine-particle episodes occurred, due to the influence of long-range transport of air masses from mainland China. PM1.0 and PM2.5 responded in similar ways; i.e., with elevated mass and OC concentrations in those episode days. During the sampling period, PM1.0 OC and EC generally behaved similarly to the carbonaceous aerosols in PM2.5, regardless of seasonal variations and influence by regional pollutions. The low and relatively constant OC/EC ratios in PM1.0 and PM2.5 indicated that vehicular emissions were major sources of carbonaceous aerosols. PM1.0 and PM2.5 had the same dominant sources of vehicular emissions in winter, while in spring PM2.5 was more influenced by PM1-2.5 (particles 1-2.5 mu m in diameter) that did not form from vehicle exhausts. Therefore, PM1.0 was a better indicator for vehicular emissions at the Roadside Station.